Ignoring Star Trek fans, astronomers name Pluto's moons

Even though 'Vulcan' was the top choice among voters, the International Astronomical Union opted to go with the second- and third-most-popular proposed names. Pluto's fourth and fifth moons are now officially known as Kerberos and Styx.

NASA/AP/File

This 2006 image from the Hubble Space Telescope shows Pluto and three of its five moons. The International Astronomical Union announced that the 'Kerberos' and 'Styx' are the names of the fourth and fifth moons.

But the IAU opted to go with the second and third choices, each of which received less than 100,000 votes, and the official names of P4 and P5 are now Kerberos and Styx, respectively.

Even though "Vulcan" hewed to the IAU's rule that the name had to come from classical mythology – in addition to being the name of Mr. Spock's homeworld, Vulcan is also the name of the ancient Roman god of fire and metalworking – the IAU had its own reasons to reject it. From their press release:

The name Vulcan had already been used for a hypothetical planet between Mercury and the Sun. Although this planet was found not to exist, the term “vulcanoid” remains attached to any asteroid existing inside the orbit of Mercury, and the name Vulcan could not be accepted for one of Pluto’s satellites (also, Vulcan does not fit into the underworld mythological scheme).

The second-most-popular name among voters was actually "Cerberus" the Roman spelling of the polycephalic hell hound. But there is already a near-Earth asteroid named 1865 Cerberus, so they changed it to the Greek spelling, "Kerberos." Styx is the name of the underworld goddess of hate who guards the river (also named Styx) separating the worlds of the living and the dead.

Kerberos has an estimated diameter of eight and 21 miles. Styx is thought to be irregularly shaped and is six to 15 miles across. Pluto's other known moons are called Charon, Nyx, and Hydra, all after figures from the ancient Greek mythological underworld.

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As expected, Mr. Shatner was not happy with the results. In a tweet that would make his first officer proud, he pointed out the illogic of accepting "Cerberus" even though it is already the name of an asteroid, but rejecting "Vulcan" because it was once the name of a planet that was hypothesized to exist but turned out not to.